U.S. patent number 6,095,942 [Application Number 09/356,507] was granted by the patent office on 2000-08-01 for speed change control device for vehicular continuously variable transmission.
This patent grant is currently assigned to Honda Giken Kogyo Kabushiki Kaisha. Invention is credited to Hirotoshi Inoue, Eiji Kitsutaka, Daihei Teshima, Masaaki Yamaguchi.
United States Patent |
6,095,942 |
Yamaguchi , et al. |
August 1, 2000 |
Speed change control device for vehicular continuously variable
transmission
Abstract
In a continuously variable transmission, a speed change control
device includes a vehicle speed sensor, a brake sensor, a release
vehicle speed memory which, when the brake is operated, renews and
stores the brake release vehicle speed, and a gradient sensor for
detecting a running road gradient. When, in an engine brake running
state, the present vehicle speed is higher than the brake release
vehicle speed stored in the release vehicle speed memory, a speed
change target value is obtained according to the difference between
the present vehicle speed and the brake release vehicle speed and
to the road gradient. And, when, in the same state, the present
vehicle speed is lower than the brake release vehicle speed, the
speed change target value is obtained according to the road
gradient. The speed change control is carried out so as to obtain
the speed change target value.
Inventors: |
Yamaguchi; Masaaki (Saitama,
JP), Kitsutaka; Eiji (Saitama, JP),
Teshima; Daihei (Saitama, JP), Inoue; Hirotoshi
(Saitama, JP) |
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
16925261 |
Appl.
No.: |
09/356,507 |
Filed: |
July 19, 1999 |
Foreign Application Priority Data
|
|
|
|
|
Aug 18, 1998 [JP] |
|
|
10-231550 |
|
Current U.S.
Class: |
477/40;
477/901 |
Current CPC
Class: |
F16H
61/66259 (20130101); B60W 2540/12 (20130101); B60W
2710/0644 (20130101); F16H 2059/663 (20130101); B60W
2552/15 (20200201); Y10T 477/621 (20150115); Y10S
477/901 (20130101) |
Current International
Class: |
F16H
61/66 (20060101); F16H 61/662 (20060101); B60K
041/12 () |
Field of
Search: |
;477/40,901 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wright; Dirk
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas, PLLC
Claims
What is claimed is:
1. A speed change control device for a vehicular continuously
variable
transmission which transmits the output of an engine thus changed
to drive wheels in a state of a continuously variable change speed,
said control device comprising:
vehicle speed detecting means for detecting a vehicle speed;
throttle opening degree detecting means for detecting a throttle
opening degree;
brake operation detecting means for detecting a brake
operation;
brake vehicle speed memory means which, when the brake operation is
detected by said brake operating detecting means, renews and stores
the vehicle speed as a brake release vehicle speed which is
detected by said vehicle speed detecting means when the brake is
operated; and
gradient detecting means for detecting the gradient of a road on
which a vehicle runs,
wherein, in the case where the fact that the brake is not operated
is detected by said brake operation detecting means, and the fact
that a throttle is substantially fully closed is detected by said
throttle opening degree detecting means,
when the present vehicle speed detected by said vehicle speed
detecting means is higher than the brake release vehicle speed
stored in said brake vehicle speed memory means,
a speed change target value is obtained according to the difference
between said present vehicle speed and said brake release vehicle
speed, and to the road gradient detected by said gradient detecting
means, and
in the same case, when the present vehicle speed detected by said
vehicle speed detecting means is lower than the brake release
vehicle speed stored in said brake vehicle speed memory means,
the speed change target value is obtained according to the road
gradient detected by said gradient detecting means, and speed
change control is carried out so as to obtain the speed change
target value.
2. A speed change control device according to claim 1, further
comprising:
a map memory means storing a plurality of maps corresponding to the
road gradients,
wherein the map corresponding to the road gradient detected by said
gradient detecting means is selected, a target engine speed is
determined from the present vehicle speed and the throttle opening
degree on the selected map, and
when the present vehicle speed detected by said vehicle speed
detecting means is higher than the brake release vehicle speed
stored in said brake vehicle speed memory means,
the speed change target value is obtained from the target engine
speed and a brake correction amount corresponding to the difference
between said present vehicle speed and said brake release vehicle
speed,
when the present vehicle speed detected by said vehicle speed
detecting means is lower than the brake release vehicle speed
stored in said brake vehicle speed memory means,
the speed change target value is obtained from the target engine
speed.
3. A speed change control device according to claim 2, wherein the
brake correction amount is previously set in correspondence with
the difference between said present vehicle speed and said brake
release vehicle speed.
4. A speed change control device according to claim 2, the brake
correction amount is determined in the case where the road is a
down-hill road.
5. A speed change control device according to claim 2, wherein, in
the case where the fact that the brake is operated is detected by
said brake operation detecting means, and the fact that a throttle
is substantially fully closed is detected by said throttle opening
degree detecting means, the brake correction amount is determined
in a predetermined value, and
the speed change target value is obtained by adding the brake
correction amount into the target engine speed.
6. A speed change control device for a vehicular continuously
variable transmission which transmits the output of an engine thus
changed to drive wheels in a state of a continuously variable
change speed, said control device comprising:
a vehicle speed sensor detecting a vehicle speed;
a throttle opening degree sensor detecting a throttle opening
degree;
a brake sensor detecting a brake operation;
a release vehicle speed memory which, when the brake operation is
detected by said brake sensor, renews and stores the vehicle speed
as a brake release vehicle speed which is detected by said vehicle
speed sensor when the brake is operated; and
a gradient sensor detecting the gradient of a road on which a
vehicle runs,
wherein, in the case where the fact that the brake is not operated
is detected by said brake sensor, and the fact that a throttle is
substantially fully closed is detected by said throttle opening
degree sensor,
when the present vehicle speed detected by said vehicle speed
sensor is higher than the brake release vehicle speed stored in
said release vehicle speed memory,
a speed change target value is obtained according to the difference
between said present vehicle speed and said brake release vehicle
speed, and to the road gradient detected by said gradient sensor,
and
in the same case, when the present vehicle speed detected by said
vehicle speed sensor is lower than the brake release vehicle speed
stored in said release vehicle speed memory,
the speed change target value is obtained according to the road
gradient detected by said gradient sensor, and
speed change control is carried out so as to obtain the speed
change target value.
7. A method for controlling a speed change of a vehicular
continuously variable transmission which transmits the output of an
engine thus changed to drive wheels in a state of a continuously
variable change speed, said method comprising the steps of:
determining whether or not a road on which a vehicle runs is a
down-hill road;
determining whether or not a throttle opening degree is opened;
determining whether or not a brake is operated;
calculating the difference between the present vehicle speed and a
brake release vehicle speed being a vehicle speed which is detected
when the brake is operated, in the case where the brake is not
operated and a throttle is substantially fully closed;
obtaining a speed change target value according to the difference
between the present vehicle speed and the brake release vehicle
speed, and to a road gradient, when the present vehicle speed is
higher than the brake release vehicle speed in the same case;
and
controlling the speed change to obtain the speed change target
value.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device for performing speed change
control in a vehicular continuously variable transmission which
transmits the output of the engine to the running drive wheels in a
state of a continuously variable change speed, and more
particularly to a device having a specific feature in the control
of speed change during a braking operation.
2. Description of the Related Art
In a conventional method of performing speed change control in a
vehicle on which a continuously variable transmission, a target
engine speed (rpm) is mounted in correspondence to an index
indicating the acceleration will of the driver (such as an engine
throttle opening degree, and the amount of depression of the
acceleration pedal, hereinafter, these are referred to merely as
"acceleration opening degree"), and the actual engine speed is made
close to the target engine speed (rpm). Japanese Patent Unexamined
Publication No. Sho. 59-219557 has disclosed a speed change ratio
control device in a vehicular continuously variable transmission
which performs the above-described speed change control.
In the above-described device (disclosed by Japanese Patent
Unexamined Publication No. Sho-59-219557), in the case where an
engine brake state is established, for instance, when the vehicle
runs down a slope, the speed change control is carried out in such
a manner that the vehicle speed is kept constant. In this control
operation, a vehicle speed which has been previously determined and
stored is employed, or a vehicle speed which is obtained when a
braking operation is carried out while the vehicle runs down a
slope.
The engine brake running state occurs generally when the vehicle
runs down a slope. The running performance required by the driver
depends on the gradient of the slope. Hence, it is difficult for
the above-described speed change control that the vehicle speed is
kept constant to meet the requirement provided by the driver. For
instance, one requirement is as follows: In the case where the
gradient of a slope is low, the running is made at a relatively
high speed with a small engine braking force, and in the case where
the gradient of a slope is high, the running is made at a low speed
with a great engine braking force. And, another requirement is as
follows: In the case where the slope has many corners such as a
mountain road, it is necessary to run the vehicle at a relatively
low speed, and when the vehicle runs down the straight slope, it is
required to run the vehicle at a relatively high speed.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the invention is to provide
a speed change control device for a vehicular continuously variable
transmission with which speed change control is effected in such a
manner that, when a vehicle runs down a slope, the running is
carried out according to the driver's desire with the gradient of
the slope taken into account.
The foregoing object of the invention has been achieved by the
provision of a speed change control device for a vehicular
continuously variable transmission (such as a belt-type
continuously variable transmission CVT in an embodiment of the
invention (described later)) which transmits the output of an
engine to the running drive wheels in a state of a continuously
variable change speed, which includes: vehicle speed detecting
means (such as a vehicle speed sensor in the embodiment); throttle
opening degree detecting means (such as a throttle opening degree
sensor in the embodiment); brake operation detecting means (such as
a brake sensor in the embodiment); brake vehicle speed memory means
(such as a release vehicle speed memory in the embodiment) which,
when a brake is operated, renews and stores a vehicle speed as a
brake release vehicle speed which is detected when the brake is
operated; and gradient detecting means (such as a gradient sensor
in the embodiment) for detecting the gradient of a road on which a
vehicle runs, and in which when, in the case where the fact that
the brake is not operated is detected, and the fact that a throttle
is substantially fully opened is detected, the present vehicle
speed detected by the vehicle speed detecting means is higher than
a brake release vehicle speed stored in the brake vehicle speed
memory means (that is, when a vehicle speed increases), a speed
change target value is obtained according to the difference between
the present vehicle speed and the brake release vehicle speed, and
to a road gradient detected by the gradient detecting means, and
when, in the same case, the present vehicle speed is lower than the
brake release vehicle speed (that is, when the vehicle speed
decreases), a speed change target value is obtained according to
the present road gradient, and speed change control is carried out
so as to obtain the speed change target value. As long as the brake
operation is effected, the brake vehicle speed memory means renews
and stores the current vehicle speed as a brake release vehicle
speed. Therefore, in the case where the brake operation is not
effected, the vehicle speed is stored which is provided at the time
of the brake release which occurred immediately before.
The speed change control device designed as described above,
functions as follows: Let us consider the case where, when a
vehicle runs downs a slope, the acceleration pedal is released, and
the acceleration opening degree is zeroed, so that the vehicle runs
in the engine brake mode (in an engine brake running state). In
this case, as long as, after the brake pedal is depressed and then
released, the vehicle speed is not increased, the speed change
target value (for instance a target engine speed (rpm)) is
determined according to the running road gradient. Therefore, the
speed change target value suitable for the gradient of the running
road on which the vehicle runs is determined, and the speed change
control is suitably carried out which agrees with the driver's
desire.
On the other hand, when, after the brake pedal is depressed and
then released, the vehicle speed increases, the speed change target
value is determined according to the difference between the present
vehicle speed and the brake release vehicle speed and to the
present road gradient detected by the gradient detecting means.
Therefore, in the case where the vehicle runs down a steep
down-hill gradient road in the engine brake mode, and the vehicle
speed increases, the control is carried out that corrects the speed
change control value which changes the speed change ratio to the
LOW side (for instance, the control that increases the target
engine speed (rpm)), and the engine brake force is increased, so
that the vehicle running characteristic is obtained which agrees
with the driver's desire.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing the arrangement of a
continuously variable transmission whose speed change control is
carried out by a speed change control device according to the
invention;
FIG. 2 is an explanatory diagram outlining the power transmission
system of the continuously variable transmission;
FIG. 3 is a block diagram showing the arrangement of the speed
change control device according to the invention;
FIG. 4 is a flow chart showing the contents of the speed change
control by the speed change control device of the invention;
FIG. 5 is a graphical representation indicating a speed change map
(for a slight down-hill gradient road) employed for the speed
control;
FIG. 6 is a graphical representation indicating a speed change map
(for a middle down-hill gradient road) employed for the speed
control;
FIG. 7 is a graphical representation indicating a speed change map
(for a steep down-hill gradient road) employed for the speed
control;
FIG. 8 is a flow chart for a description of the contents of a brake
correction amount calculating sub-routine in the flow chart of FIG.
4; and
FIG. 9 is a graphical representation indicating vehicle speed
deviations SV(BR) and brake correction amounts N(BR).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the invention will be described with
reference to the accompanying drawings.
FIGS. 1 and 2 show the arrangement of a belt-type continuously
variable transmission in which speed change control is carried out
by a speed change control device according to the invention.
The belt-type continuously variable transmission CVT includes: a
metal V-belt mechanism 10 arranged between an input shaft 1 and a
counter shaft 2; a planetary-gear-type forward and backward
switching mechanism 20 which is arranged between the input shaft 1
and a drive side movable pulley 1, and a main clutch 5 arranged
between the counter shaft 2 and an output member (such as a
differential mechanism 8). The continuously variable transmission
CVT is adopted for a vehicle. The input shaft 1 is coupled through
a coupling mechanism CP to the output shaft of the engine ENG, and
the drive power transmitted to the differential mechanism is
transmitted to the right and left drive wheels.
The metal V-belt mechanism 10 includes a drive side pulley 11
arranged on the input shaft 1, a driven side pulley 16 arranged on
the counter shaft 2, and a metal V-belt 15 laid over those two
pulleys 11 and 16.
The drive side pulley 11 includes a stationary pulley half 12
rotatably provided on the input shaft 1, and a movable pulley half
13 which is axially movable with respect to the stationary pulley
half 12. On a side of the movable pulley half 13, a drive side
cylinder chamber 14 is formed by being surrounded by a cylinder
wall 12a coupled to the stationary pulley half 12. An oil pressure
Pdr is supplied into the drive side cylinder chamber 14, to produce
a side pressure for moving the movable pulley half 13 axially; that
is, a drive side pulley axial thrust force.
The driven side pulley 16 includes a stationary pulley half 17
secured to the counter shaft 2, and a movable pulley half 18 which
is movable with respect to the stationary pulley half 17 axially.
On a side of the movable pulley half 18, a driven side cylinder
chamber 19 is formed by being surrounded by a cylinder wall 17a
coupled to the stationary pulley half 17. An oil pressure Pdn is
supplied into the drive side cylinder chamber 19, to provide a side
pressure for moving the movable pulley half 18 axially; that is, a
driven side pulley axial thrust force.
Hence, by suitably controlling the oil pressures Pdr and Pdn
supplied to the cylinder chambers 14 and 19, a pulley side pressure
is obtained without slip of the belt 15, and the pulleys 11 and 16
can be changed in pulley width. Accordingly, by changing the
winding radius of the V-belt 15, the change gear ratio i can be
continuously changed.
The planetary-gear-type forward and backward switching mechanism 20
has a double-pinion-type planetary gear train, and its sun gear 21
is coupled to the input shaft 1, and its carrier 22 is coupled to
the stationary pulley half 12, and its ring gear 23 can be fixedly
held by a backward brake 27. Furthermore, the mechanism 20 has a
forward clutch 25 which is able to couple the sun gear 21 and the
ring gear 23 to each other. Upon engagement of the forward clutch
25, all the gears 21, 22 and 23 are turned together with the input
shaft 1, and the drive side pulley 11 is driven in the same
direction (in the forward direction) as the input shaft 1. On the
other hand, upon engagement of the backward brake 17, the ring gear
23 is fixedly held, so that the carrier 22 is driven in the
direction opposite to the direction in which the sun gear 21 is
driven, and the drive side pulley 11 is driven in the direction
(the backward direction) opposite to the direction in which the
input shaft 1 is driven.
The main clutch 5 is to control the transmission of power between
the counter shaft 2 and the output side member, and during the
engagement thereof, the power is transmitted between the counter
shaft 2 and the output side member. And, by controlling the
engaging force, the capacity of transmission of torque (or torque
capacity) between the input side and the output side is controlled.
Therefore, at the time of engagement of the main clutch 5, the
engine output speed-changed by the metal V-belt mechanism 10 is
transmitted through gears 6a, 6b, 7a and 7b to the differential
mechanism 8, and then to the right and left wheels (not shown)
through the differential mechanism 8. When the main clutch 5 is
released, the drive power transmission is not effected, and the
speed changer is placed in the neutral state.
The speed change control device is to control the oil pressures Pdr
and Pdn in the drive side cylinder chamber 14 and the driven side
cylinder chamber 19 thereby to control the thrust forces of the
drive side pulley and the driven side pulley. That is, the speed
change control device is to suitably perform the speed change
control while setting a minimum and necessary thrust force without
belt slip. The control is carried out by the speed change control
device according to the invention. The device and the control will
be described in detail.
FIG. 3 shows the arrangement of the speed change control device.
The device includes a control valve 40 for controlling oil
pressures Pdr and Pdn applied to the drive side cylinder chamber 14
and the driven side cylinder chamber 19, and a controller 30 for
controlling the operation of the control valve 40. The controller
30 receives a detection signal from a brake sensor 31 adapted to
detect the operation of the brake, a detection signal from a
gradient sensor 32 adapted to detect the gradient of a road on
which a vehicle runs, a detection signal from a vehicle speed
sensor 33 adapted to detect a vehicle running speed, and a
detection signal from a throttle opening degree sensor 34 adapted
to detect a throttle opening degree. Furthermore, a map memory 35
storing a speed change map, and a release vehicle speed memory 36
renewing and storing a vehicle speed at the time of release of the
brake are connected to the controller 30. By using the detection
signals of the above-described sensors and the contents of the
memories 35 and 36, the operation of the control value 40 is
controlled; that is, the speed change control is carried out.
The contents of the speed change control will be described with
reference to a flow chart of FIG. 4. In the control, first an
engine throttle opening degree .theta.TH is detected with the
throttle opening degree sensor 34 (Step S1). When the engine
throttle opening degree .theta.TH.noteq.0; that is, in the state
that the acceleration is on, the throttle flag F(TH) is set to 1
(F(TH)=1); and when the detected engine throttle opening degree
.theta.TH is 0 (O.theta.H=0), that is, when the acceleration is
off, the throttle flag F(TH) is set to 0 (F(TH)=0). Furthermore, in
Step S2, the present vehicle running speed V(AC) is detected with
the vehicle speed sensor 33.
In Step S3, it is detected with the brake sensor 31 whether or not
the brake operation is effected. When the brake operation is
effected, the brake flag F(BR) is set to 1 (F(BR)=1); and when the
brake operation is not effected, the brake flag is set to 0
(F(BR)=0). And, in Step S4, the gradient of the road on which the
vehicle is running is detected with the gradient sensor 32.
And, a speed change map corresponding to the road gradient thus
detected is read from the map memory 35 (Step S5). In the map
memory 35, a plurality of speed change maps have been stored in
correspondence to road gradients. A speed change map corresponding
to the present road gradient is read from the map memory. The speed
change maps include, for instance, a speed change map for a slight
down-hill gradient (FIG. 5), speed change map for a middle
down-hill gradient (FIG. 6), a speed change map for a steep
down-hill gradient (FIG. 7), a speed change map for a horizontal
flat road (not shown), and speed change maps for various up-hill
gradients. Those maps have been previously determined and stored.
Among those speed change maps, one corresponding to the present
road gradient is read. En the speed change maps, as shown in FIGS.
5 through 7, target engine speeds (rpm) Neo are determined
according to engine throttle opening degrees .theta.TH and vehicle
speeds. From this map, a target engine speed Neo is read which
corresponds to the present vehicle speed V(AC) and the actual
engine throttle opening degree .theta.TH.
Next, in Step S6, an amount of correction of a target engine speed
Neo, namely, a brake correction amount N(BR) is calculated. The
content of calculation in Step S6 is as shown in FIG. 8, a flow
chart, and will be described with reference to FIG. 8.
First, in Step S11, it is determined whether or not the present
road gradient is of down-hill gradient. The brake correction amount
N(BR) is a value which is set when the vehicle runs down a road (a
down-hill gradient road). Therefore, in the case where it is
determined that the road is flat and horizontal or of up-hill
gradient, then Steps S12, S13 and S14 are effected. That is, the
vehicle speed deviation SV(BR) is set to zero (SV(BR)=0), the brake
release vehicle speed V(BR) is set to zero (V(BR)=0), and the brake
correction amount N(BR) is also set to zero (N(BR)=0). In other
words, those values are reset, and the operation (flow) is
ended.
On the other hand, when it is determined that the road is of
down-hill gradient, Step S15 is effected. In Step S15, it is
determined whether or not the throttle flag F(TH) is zero (0); that
is, it is detected whether or not the acceleration is off. When,
even if the road is of down-hill gradient, the acceleration is on;
that is, the acceleration pedal is depressed, the driver's will is
of acceleration, and therefore in this case, too, Steps S12, S13
and S14 are effected, so that the vehicle speed deviation SV(BR) is
set to zero (SV(BR)=0), the brake release vehicle speed V(BR) is
set to zero (V(BR)=0), and the brake correction amount N(BR) is
also set to zero (N(BR)=0). Thus, the operation (flow) is
ended.
In the case where the acceleration is off (.theta.TH=0) while the
vehicle runs down the down-hill gradient road, Step S16 is
effected, so that it is determined whether or not the brake flag
F(BR) is 1; that is, it is determined whether or not the brake is
operated. When F(BR)=1; that is, when the brake is operated, the
vehicle speed deviation SV(BR) is set to 0 (Step S17), and the
present vehicle speed V(AC) detected by the vehicle speed sensor 33
is renewed and set as a brake release vehicle speedV(BR). And, a
constant value YN (for instance 300 rpm) is set as a brake
correction amount N(BR). The constant value YN is a value which is
set to increase the target engine speed Neo to an extent when the
brake is operated.
Thereafter, when the brake operation is released, in the next
routine the operation is advanced from Step 16 to Step 20, so that
it is determined whether or not the brake release vehicle speed
V(BR) is 0. The brake release vehicle speed V(BR) is 0 until the
brake is operated. In this case, the operation (flow) is ended. On
the other hand, in the case where the brake is operated at least
once, and then the brake release vehicle speed V(BR) is set, Step
S21 is effected. In Step S18, since the actual vehicle speed V(AC)
is renewed and stored, the vehicle speed detected by the vehicle
speed sensor 33 at the time of release of the brake is stored, as a
brake release vehicle speed V(BR), in the release vehicle speed
memory 36.
In Step S21, the vehicle speed deviation SV(BR) between the brake
release vehicle speed V(BR) stored in the release vehicle speed
memory 36 and the present vehicle speed V(AC) detected by the
vehicle speed sensor 33 is calculated; and in Step S22, it is
determined whether or not the vehicle speed deviation SV(BR) is
equal to or larger than 0 ((SV(BR).gtoreq.0). When
(SV(BR).gtoreq.0; that is, when the vehicle speed increases, Step
S23 is effected, so that a brake correction amount N(BR)
corresponding to the vehicle speed deviation SV(BR) is obtained.
The brake correction amount N(BR) is a value for correctively
increasing the target engine speed Neo, and is pre-set in
correspondence to the vehicle speed deviation SV(BR) in advance, as
shown in FIG. 9. And, in Step S23, from the table thus determined,
a brake correction amount N(BR) corresponding to the present
vehicle speed deviation SV(BR) is obtained. When SV(BR)<0; that
is, when the vehicle speed decreases, Step S14 is effected, so that
the brake correction amount N(BR) is set to 0.
When the brake correction amount N(BR) is obtained in the
above-described manner, Step S7 (FIG. 4) is effected. In Step S7,
the brake correction amount N(BR) is added to the target engine
speed Neo read from the speed change map in Step S5 and
corresponding to the present vehicle speed V(AC) and the actual
engine throttle opening degree .theta.TH, thereby to correct the
target engine speed Neo.
When the target engine speed Neo thus corrected is obtained, the
speed change control is so carried out that the present engine
speed Nea is equal to the corrected target engine speed Neo.
Specifically, in step S8, the oil pressures Pdr and Pdn of the
drive side and driven side cylinder chambers 14 and 19 are
controlled with the control valve 40; that is, the speed change
control is carried out.
In the above-described embodiment, the technical concept is applied
to the metal V-belt type continuously variable transmission;
however, the invention is not limited thereto or thereby; that is,
the technical concept of the invention may be applied to
continuously variable transmissions of other types.
As was described above, according to the invention, when, in the
engine brake running mode, the present vehicle speed is higher than
the brake release vehicle speed stored in the brake vehicle speed
memory means (that is, the vehicles speed increases), the speed
change target value is obtained according to the difference between
the present vehicle speed and the brake release vehicle speed and
to the present road gradient detected by the gradient detecting
means. Therefore, in the case where, for instance, the vehicle runs
down the down-hill gradient road in the engine brake running mode
with the acceleration pedal released and with the acceleration
opening degree zeroed (that is, in the engine brake running state),
as long as the vehicle speed is not increased after the brake pedal
is depressed and then released, the speed change target value (for
instance, the target engine speed (rpm)) is determined according to
the running road gradient; that is, the speed change target value
is determined which is suitable for the gradient of the road on
which the vehicle runs. Thus, the speed change control is suitably
carried out which agrees with the driver's desire.
On the other hand, in the case where, in the engine brake running
state, the present vehicle speed is lower than the brake release
vehicle speed (that is, when the vehicle speed decreases), the
speed change target value is obtained from the present road
gradient. Therefore, when the vehicle speed increase after, in the
engine brake running state, the brake pedal is depressed once and
then released, the speed change target value is determined
according to the difference between the present vehicle speed and
the brake release vehicle speed and to the present road gradient
detected by the gradient detecting means, so that the vehicle runs
down the steep down-hill gradient road in the engine brake mode.
However, in the case where the vehicle speed increases, the control
is carried out that corrects the speed change control value which
changes the speed change ratio to the LOW side (such as the control
that increases the target engine speed); that is, the engine brake
force is increased to perform the speed change control having the
vehicle running characteristic which agrees with the driver's
desire.
The present disclosure relates to the subject matter contained in
Japanese patent application No. Hei. 10-231550 filed on Aug. 18,
1998 which is expressly incorporated herein by reference in its
entirety.
* * * * *